[LV] Use value_or to simplify code. NFC (#77030)

Author: topperc

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -5004,9 +5004,8 @@ VectorizationFactor LoopVectorizationPlanner::selectVectorizationFactor(
     VectorizationFactor Candidate(i, C.first, ScalarCost.ScalarCost);
 
 #ifndef NDEBUG
-    unsigned AssumedMinimumVscale = 1;
-    if (std::optional<unsigned> VScale = getVScaleForTuning(OrigLoop, TTI))
-      AssumedMinimumVscale = *VScale;
+    unsigned AssumedMinimumVscale =
+        getVScaleForTuning(OrigLoop, TTI).value_or(1);
     unsigned Width =
         Candidate.Width.isScalable()
             ? Candidate.Width.getKnownMinValue() * AssumedMinimumVscale